A quick way to check if its a Roadster is the shape of the front frame of the chassis
...if the upper corners stick out then its probably a Ron Champion based chassis , maybe a Mcsorley chassis which is wider than a "Book " chassis ( this being the Ron Champion chassis) & altered to accept the Independant rear suspension of the Sierra running gear.
The Front Frame of a Roadster is quite different to the Ron Champion version.
cheers
andy